Sensex gains 21 pts to close at 18,021Continuing its winning spree for the seventh straight session, the Sensex at the Bombay Stock Exchange rose a modest 21 points, or 0.1 percent, to a seven-month closing high of 18,021, today. The Nifty at the National Stock Exchange rose 4 points, or 0.1 percent, to 5,435.